Charging method in telecommunications network

ABSTRACT

A method and system for charging a subscriber ( 10 ) in a telecommunications network comprising nodes ( 11  and  12 ) connected to a mediator unit ( 14 ), whereby a billing unit ( 15 ) comprising the subscriber&#39;s ( 10 ) charging data can be located outside the network used, preferably in the subscriber&#39;s ( 10 ) home network, in a subscriber identity module (SIM) or behind an open service architecture (OSA) associated with the network, the method comprising the following steps of: noting in the nodes ( 11  and  12 ) the event data related to the services used by the subscriber ( 10 ) and reporting the event data to the mediator unit ( 14 ), the event data being converted substantially in real time in the mediator unit ( 14 ) by applying the network charging algorithms to provide a charging data format understandable to the billing unit ( 15 ), expressed preferably as an amount of money spent or as charging pulses, for the updating of the subscriber&#39;s ( 10 ) charging data between the mediator unit ( 14 ) and the billing unit ( 15 ).

This application is the National Phase of International ApplicationPCT/FI99/00858 filed Oct. 18, 1999 which designated the U.S. and thatInternational Application was Published under PCT article 21(2) inEnglish.

BACKGROUND OF THE INVENTION

The invention relates to charging in a telecommunications network andparticularly to real-time charging of prepaid services.

The GPRS (General Packet Radio Service) is a new service in the GSMsystem and one of the objects of the standardization work in the GSMphase 2+ at the ETSI (European Telecommunication Standard Institute).The GPRS operational environment comprises one or more subnetworkservice areas interconnected by a GPRS Backbone Network. A subnetworkcomprises a number of packet data service nodes, referred to as GPRSsupport nodes, each of which is connected to the GSM mobile network insuch a way that it can provide a packet service for mobile dataterminals via several base stations, i.e. cells. The intermediate mobilecommunications network provides circuit-switched or packet-switched datatransmission between a support node and mobile data terminals. Differentsubnetworks are in turn connected to an external data network, to apublic switched packet data network PSPDN, for example. The GPRS servicethus allows packet data transmission to be provided between mobile dataterminals and external data networks, with the GSM network serving as anaccess network.

In the GPRS system, charging is based on a plural number of chargingrecords CDR generated at the support nodes, the records beingtransmitted to a charging gateway functionality CGF. From the data itreceives, the charging gateway functionality filters the charging dataand transmits the filtered charging records CDR to a billing system thatgenerates the actual charging data. A problem with the above describedarrangement is that the generating of the charging data is relativelyslow. In particular, when a subscriber uses what are known as prepaidservices, charging should take place substantially in real-time to avoida situation where the subscriber could continue to use the prepaidservice even though the amount paid in advance by the subscriber hadalready been exhausted. One solution to the problem is to send thefiltered charging data directly from the charging gateway functionalityto the billing unit. The term ‘billing unit’ in this context refersgenerally to a functional unit that maintains the subscriber's chargingdata, or account data, and also comprises, for example, informationabout the advance payments made by the subscriber for the prepaidservices. Alternatively, also data about the GPRS context events couldbe sent from the support nodes to the billing unit, charging being thenbased on the context events. In the above cases, problems arise, on onehand, from the complexity and amount of data received from the supportnodes and, on the-other hand, from network-specific charging methodsthat may differ from one another. Charging can be based, for example, onthe duration of the service, on the amount of data to be transferred, oron other similar criteria. If the subscriber uses a foreign network, thebilling unit must know the charging algorithms of the network concerned;this renders the billing unit configuration complex. Similar problemscan also arise in a circuit-switched network, such as the GSM network,and in broadband networks. In the GSM system, for example, differentevents taking place during a call can have a different impact oncharging, depending on the operator, or they may have no impact at all.Such events include quality of service changes, transmission ratechanges, location changes, temporary entry into a shadow region,temporary cutting off of the subscriber connection, and changes duringan ongoing call in the services used.

BRIEF DESCRIPTION OF THE INVENTION

An object of the invention is therefore to provide a method and a systemimplementing the method in such a way that the above problems can besolved. The objects of the inventions are achieved with a method andsystem characterized by what is stated in the independent claims 1 and11. The preferred embodiments of the invention are disclosed in thedependent claims.

The invention is based on the idea of providing telecommunicationsnetwork nodes with a function that converts event data or charging datareceived from the nodes, by applying the network charging algorithms, toprovide a real-time, unambiguous charging data format understandable tothe subscriber's billing unit, expressed as an amount of money spent oras charging pulses, for example. A node in this context refers to anetwork element, such as a packet network support node GSN or a mobileservices switching centre MSC, that provides event data having an impacton charging. Unambiguity means that the charging data are structurallyidentical in the different telecommunications networks, irrespective ofthe internal charging algorithms of the networks. The unambiguouscharging data are further transmitted to the subscriber's billing unitthat maintains in real-time the subscriber's charging data. The functionassociated with the network nodes can also negotiate with thesubscriber's billing unit about charging; for example, the billing unitprovides a predetermined amount of the prepaid sum for use to thefunction associated with the nodes of the network used and when theamount is exhausted, the function can request an additional payment foruse.

The method and system of the invention provide the advantage that thesubscriber's charging data can be updated in a real-time process, thusallowing prepaid services to be used. In addition, the invention allowsthis irrespective of the network used, the charging data of a visitingsubscriber thus being also updated substantially in real-time in thehome network or a subscriber identity module, for example. The billingunit only needs to know one common charging data structure; eachfunction integrated into the support nodes of a telecommunicationsnetwork knows the corresponding charging algorithm of the network.Another advantage of the invention is the possibility to optimize theamount of signalling related to the charging data because data on allseparate events having an impact on the call rate do not need to betransmitted all the way to the billing unit.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following the invention will be described in greater detail inconnection with preferred embodiments and with reference to theaccompanying drawings, in which

FIG. 1 is a block diagram illustrating a system of the invention forcarrying out charging in a packet-switched telecommunications networkaccording to a preferred embodiment, and

FIG. 2 is a block diagram illustrating a system of the invention forcarrying out charging in a circuit-switched telecommunications networkaccording to a preferred embodiment.

DETAILED DESCRIPTION OF THE INVENTION

Although the use of the invention will be described below with referenceto the GPRS and GSM systems, the description does not in any wayrestrict the application of the invention in other telecommunicationsnetworks.

FIG. 1 illustrates a typical arrangement in a GPRS network. It is to beunderstood, however, that the Figure only shows components relevant tothe invention. The architecture of GPRS networks is not as mature asthat of the GSM networks. All GPRS terms should therefore be understoodas being descriptive rather than limiting. The arrangement in the Figurecomprises a separate Serving GPRS Support Node (SGSN) 11 of the GPRS.The support node 11 controls certain operations of the packet radioservice on the network side. The operations include logging on and offthe system by subscribers 10, routing area updates of the subscribers10, and data packet routing to correct destinations.

The intermediate mobile network (not shown) provides packet-switcheddata transmission 31 between the support node 11 and the mobilesubscribers 10. Different sub-networks, in turn, are connected 33 to anexternal data network 13, such as the Internet, via a specific GatewayGPRS Support Node GGSN 12. Packet data transmission between the mobilesubscriber 10 and the external data networks 13 is thus accomplished bymeans of the GPRS service, with the GSM network functioning as an accessnetwork. The GGSN comprises, for example, routing information of GPRSsubscribers, i.e. SGSN addresses and charging data. The SGSN and GGSNfunctionalities can be integrated into one and the same physical node.

The GPRS network of FIG. 1 comprises one serving GPRS support node SGSN(11) and one GPRS gateway support node GGSN (12). The different supportnodes SGSN (11) and GGSN (12) are interconnected 32 via anintra-operator backbone network. It is to be understood that a GPRSnetwork may comprise any number of support nodes 11 and gateway supportnodes 12.

Each support node 11 manages a packet data service in the area of one ormore cells in a cellular packet radio network. To achieve this, eachsupport node 11 is connected to a certain local part of the GSM system(not shown in FIG. 1), typically to a mobile services switching centre,but in some situations it may be preferable to connect it directly to abase station subsystem BSS, i.e. to a base station controller BSC or abase station BTS. A subscriber 10 in a cell communicates with a basestation BTS over a radio interface and further through the mobilenetwork with the support node 11 to the service area of which the cellbelongs. In principle, the mobile network between the support node 11and the subscriber 10 only transmits 31 packets between these two. Forthis purpose, the mobile network can offer either a circuit-switchedconnection or packet-switched data packet transmission between thesubscriber 10 and the serving support node 11. It should be noted,however, that the mobile network only provides a physical connectionbetween the subscriber 10 and the support node 11, and that its exactoperation and structure are not relevant to the invention. Theconnection 31 between the subscriber 10 and the support node 11 can alsobe a fixed one.

An intelligent network IN is a network architecture connected to thebasic network (the GPRS, for example), enabling faster, easier and moreflexible service implementation and service control. This is performedby transferring the service control from the telephone exchange to aseparate functional unit of the intelligent network. The services thusbecome independent of the basic network operation, and the basic networkstructure and software do not have to be changed when services arealtered or added. In addition to the actual network operator, anintelligent network may comprise several service providers.

In fixed networks, intelligent network standardization has progressedrapidly in recent years. These standards define a certain functional andhierarchical model for the intelligent network. In the intelligentnetwork model, service control has been transferred from the exchange ofthe basic network to a service control point (SCP) in the intelligentnetwork. The SCP comprises the required database and service logicprograms (SLP), in other words the software to provide the logicstructure of a particular service (service logic), i.e. the servicecontrol point SCP provides a service control function (SCF). A serviceswitching point (SSP) is an exchange, for instance a basic networkexchange providing the service switching function (SSF), in other wordsthe identification of the intelligence network service and thetriggering of interaction with the service control point (SCP). Forexample, when a call associated with an intelligent network service isset up, the service switching point SSP takes care of establishing theconnection. To provide the intelligent network service, the serviceswitching point SSP inquires instructions of the service control pointSCP when encountering detection points associated with intelligentnetwork services. In other words, the service switching point SSPtransfers the control to the SCP and remains waiting for the SCP'soperations. When the intelligent network service is triggered, a servicelogic program SLP is initiated at the service control point SCP, theoperation of the program determining the instructions the SCP sends tothe SSP at each call stage. The SSP interprets the instructions itreceives and initiates the required call control operations. In otherwords, the triggering of an intelligent network service means that anintelligent network service function is initiated by the impact of animpulse caused when a specific identification requirement is met.

One way to integrate intelligent network functions into the GPRS networkis to arrange the nodes SGSN (11) and GGSN (12) of the GPRS system tofunction as intelligent network switching points SSP. A switching pointSSP provides the service switching function SSF. The service controlpoint SCP, or a similar physical entity, providing the service controlfunction SCF 14 and 15 is usually a separate functional unit.

Intelligent network components are interconnected via a signallingnetwork conforming to the signalling system number 7 (SS7, SignallingSystem Number 7 is a well-known signalling system described in therecommendations of the CCITT (now the ITU-T)). When communicating witheach other, intelligent network components use, for example, the INAPprotocol (Intelligent Network. Application Protocol described in theETSI (European Telecommunications Institute) standard ETSI IN CS1 INAPPart 1: Protocol Specification, prETS 300 374-1). In the SS7 protocolstack the INAP layer is the topmost layer, situated on top of a TCAPlayer (Transaction Capabilities Application Part), an SCCP layer(Signalling Connection Control Point) and an MTP layer (Message TransferPart). In the GSM and the GPRS, components communicate using for examplea CAP protocol GSM 09.78 or a MAP protocol GSM 09.02.

When the subscriber 10 registers in the GPRS network, i.e. in a GPRSattach procedure, the SGSN 11 creates a mobility management context (MMcontext) 21 containing information related to the mobility and securityof the subscriber 10, for example. In connection with a PDP activationprocedure the SGSN 11 creates a PDP context (packet data protocol), 22and 23 to be used for routing purposes, with the GGSN 12 used by theGPRS subscriber 10, within the GPRS network. The PDP context determinesdifferent data transmission parameters, such as PDP type (X.25 or IP,for example), PDP address (X.121 address, for example), Quality ofService QoS and NSAPI.

The GPRS gateway support node GGSN 12 connects the GPRS network to thedata networks 13, such as an IP network (the Internet). The GGSN 12includes the PDP addresses and routing information, i.e. the PDPcontexts 24 and 25, of the GPRS subscribers 10. The routing informationis used for tunneling protocol data units PDU from the data network 13to the current switching point of the subscriber 10, i.e. to the servingSGSN 11.

According to the method of the invention, an intelligent network servicecontrol function (M-SCF) 14 or another similar mediator unit function isconnected to the packet network nodes 11 and 12. From the support nodes11 and 12 information about different context events 21 to 25 related tothe services used by the subscriber 10 is submitted to the mediator unit14. In an intelligent network application the information provides theservice control function SCF with impulses triggering the service. Themediator unit 14 converts in real time the information received from theMM and PDP contexts 21 to 25 by applying the charging algorithms of thenetwork to provide unambiguous charging data expressed as an amount ofmoney spent or as charging pulses, for example. The network-specificcharging algorithms may be based, for example, on the duration of theservice used, the amount of data transferred and the quality of service,In addition, the charging algorithm may be subscriber-specific, in whichcase it can be loaded to the mediator unit 14, at 15 when necessary,from the home network of the subscriber 10 in connection with locationupdating, for example. The subscriber-specific charging algorithm canalso exchange information with the charging algorithm of a visitednetwork or with another corresponding service responsible for thedetermining of mediator unit charging. The determining of the chargingof a connection established to a selected number, for example, can beadvantageously left at the mediator unit's responsibility because thevisited network knows the charging principles of the addresses in itsarea, for example. Alternatively, if the packet network is provided witha charging gateway functionality CGF (not shown), the mediator unit 14is advantageously located in association with the CGF; it thus receivesthe CDR data coming from the support nodes 11 and 12 and filtered by theCGF. Also in this case the mediator unit 14 converts in real time theinformation it receives by applying the charging algorithms of thenetwork to provide unambiguous charging data, expressed as an amount ofmoney spent or as charging pulses, for example.

The charging data are forwarded to the subscriber billing entity 15,which is advantageously an intelligent network service control function(H-SCF). The billing unit 15 is located, for example, in the homenetwork of the subscriber 10, in a subscriber identity module (SIM), orin another similar location determined on the basis of subscriberidentity. The billing unit 15 can also be located behind an open servicearchitecture (OSA) associated with the GPRS, GSM or UMTS (UniversalMobile Telecommunications System), whereas the mediator unit 14 islocated within the area of a GPRS, GSM or UMTS network, preferably in aCSE (Camel Service Environment) of the home network. The open servicearchitecture provides an entity-based interface for service featuresthat are used for providing services. The open service architecture canbe provided either from the CSE or from a server communicating with theCSE for the purpose of providing service features. To implement theservice features provided by the open service architecture within thenetwork, the network support nodes are controlled by applyingnetwork-specific operations (such as CAP, INAP, MAP, ISUP) typicallyfrom the CSE, for example. The open service architecture is defined inthe ETSI UMTS recommendation 23.20. The billing unit 15 comprises theaccount data of the subscriber 10 and it updates the data in real timeon the basis of the information it receives from the mediator unit 14.Since the billing unit 15 receives the charging data in an unambiguousform, it does not need to know the charging algorithms of the differentpacket networks that the subscriber 10 possibly visits.

For prepaid services the billing unit 15 comprises a particularprepayment account into which the subscriber 10 can make a prepayment.The billing unit 15 debits the prepayment account, on the basis of theinformation it has received from the mediator unit 14, with the amountof the prepaid services used by the subscriber 10. If the amount ofmoney in the prepayment account has been exhausted, the billing unit 15informs this to the packet network which prevents the subscriber fromusing the services for example by deactivating the contexts 21 to 25 ofthe subscriber 10 in the support nodes 11 and 12.

In another alternative for performing charging when prepaid services areused the mediator unit 14 requests the billing unit 15 to place apredetermined amount of the money in the prepayment account at itsdisposal and from the sum it receives, the mediator unit 14 thensubtracts the amount corresponding to the services used by thesubscriber 10. If the subscriber stops using a service, therebydeactivating for example the MM or PDP context 21 to 25, thecorresponding amount of money that is left is transferred back into theprepayment account at the billing unit 15. On the other hand, if theamount of money transferred to the mediator unit 14 is exhausted, themediator unit 14 requests a new sum from the billing unit 15. If theprepayment account at the billing unit 15 is exhausted, and a new sumcannot be transferred from the billing unit 15 to the mediator unit 14,the subscriber 10 is prevented from using the services.

When prepaid services are charged for, a certain amount of credit mayalso be accepted. In this case the subscriber 10 can use the serviceseven after the prepayment has been exhausted.

In a preferred embodiment of the invention a first context eventfulfilling the trigger conditions and associated with a session of thesubscriber 10 or with a particular context 21 to 25 of a session of thesubscriber 10 triggers the intelligent network service in the servicecontrol function 14 acting as the mediator unit function. The servicecontrol function 14 acting as the mediator unit function determines thecharging algorithm to be applied. The charging algorithm provides thecontext events that are significant for charging. After the chargingalgorithm has been determined the mediator unit function 14 informs thesupport node 11 or 12 the context events it is interested in andrequests a report of the events. The report is recurrently provided onthe events concerned in association with one and the same session orcontext 21 to 25, without a separate request, for as long as the context21 to 25 or the session is active. In another preferred embodiment ofthe invention the mediator unit function 14 triggers an intelligentnetwork service in the billing entity 15 when a first intelligentnetwork service of a particular subscriber 10 at a particular moment istriggered in the mediator unit function by a context event. Theintelligent network service initiated in the billing entity 15 as aresult of the triggering then checks the account of the subscriber 10and if there is no money left in the account, it deactivates the context21 to 25 that performed the triggering and prevents the generating ofnew contexts 21 to 25.

In another preferred embodiment of the invention, the context 21 to 25that performed the triggering is deactivated by submitting adeactivation request from the service control function 15 to the supportnode 11 or 12, either via the mediator unit function 14 or directly. Inyet another preferred embodiment of the invention the context 21 to 25that performed the triggering is deactivated and the activation of newcontexts is prevented by submitting a request for the deactivation ofthe contexts 21 to 25 to the home location register (HLR, not shown),the contexts 21 to 25 then being deactivated and the activation of newcontexts prevented via the HLR in accordance with GPRS recommendations.

In another preferred embodiment of the invention the billing entity 15submits part of the sum prepaid by the subscriber 10 to the mediatorunit function 14 when an intelligent network service associated with thesubscriber 10 in question is triggered in the billing entity function.

According to yet another preferred embodiment of the invention, an IPprotocol stack (Internet Protocol) is used at an interface 42 betweenthe mediator unit 14 and the support node 11 and 12, and an SS7 protocolstack at an interface 41 between the mediator unit 14 and the billingunit 15. The interface 42 between the mediator unit 14 and the supportnode 11 and 12 is advantageously based on CORBA architecture (CommonObject Request Broker Architecture) or on another entity-baseddistributed architecture. CORBA is an architecture defined by ObjectManagement Group. To put it simply, CORBA allows applications tocommunicate with each other irrespective of where the applications arelocated or who designed them. It is an architecture that provides arough basis for open environments based on standards and capable ofgrowing as the operator's requirements increase.

FIG. 2 shows the operation of the invention in a circuit-switched GSMmobile communication network. It is apparent that the circuit-switchednetwork can also be implemented by using fixed connections, for example.The network comprises a base station subsystem (BSS) 112. The BSS 112and subscribers 110 communicate over radio connections 131. In the basestation subsystem 112 each cell is served by a base station (BTS) 116. Anumber of base stations 116 are connected to a base station controller(BSC) 117, the function of which is to control radio frequencies andchannels used by the BTS 116. The BSC 117 is connected to a mobileservices switching centre (MSC) 111. The MSC in turn is connected toother telecommunications networks, such as the public telephone network(PSTN) 113. The Figure only shows network elements that are necessaryfor the understanding of the invention. The number of network elementsmay be arbitrary. 30 The operation of the invention in acircuit-switched network basically corresponds to the above describedoperation of the invention in a packet-switched network. The networkelement, or node, corresponding to the support node 11 and 12 andproviding event data for charging is the mobile services switchingcentre (MSC) 111, for example. The mobile services switching 35 centre111 comprises a basic call state model (BCSM) 121, which describes thedifferent phases of call control. The mobile services switching centre111 is advantageously associated with an intelligent network switchingpoint SSP, the data related to a session of a subscriber 110 or to aparticular state model 121 of a session of the subscriber 110 thenproviding impulses for the service control function SCF and triggeringthe intelligent network service in the service control function 114acting as the mediator unit function. The operation of the mediator unit114 corresponds to that of the mediator unit 14 described in connectionwith the packet-switched network. Similarly, the operation of a billingunit 115 corresponds to that of the billing unit 15 described above inconnection with the packet network. According to a preferred embodimentof the invention, an IP protocol stack (Internet Protocol) is used at aninterface 142 between the mediator unit 114 and the node 111 and,further, an SS7 protocol stack at an interface 141 between the mediatorunit 114 and the billing unit 115. The interface 142 between themediator unit 114 and the node 111 is advantageously based on the CORBAarchitecture or on another entity-based, distributed architecture.

The mediator unit 114 can be located in the node 111, or as a separateunit. Several mediator units may be used: for example, when a call istransmitted via several nodes 111, a separate mediator unit 114 isprovided for each node 111 or, alternatively, several nodes 111 use oneand the same mediator unit 114. A plurality of nodes 111 may beassociated with a call of the subscriber 110 when the subscriber 110moves within a visited network area, for example, where the subscriber110 is served by a visited network centre VMSC (not shown), whichcomprises a mobile services switching centre MSC and a visitor locationregister VLR (VMSC=VLR+MSC), the call being forwarded from the VMSC to agateway mobile services switching centre GMSC (not shown) which isconnected to other telecommunications networks, such as the publictelephone network PSTN, and which comprises gateway functionality forcalls entering and leaving the networks.

It is apparent to a person skilled in the art that as technologyadvances the basic idea of the invention can be implemented in variousdifferent ways. The invention and its embodiments are therefore notlimited to the above described examples, but they may vary within thescope of the claims.

What is claimed is:
 1. A method for charging a subscriber in a visitedtelecommunications network being other than a home network of thesubscriber, the visited network comprising nodes connected to a mediatorunit, whereby a billing unit comprising the subscriber's charging datais located outside the visited network, the method comprising: noting intelecommunications network nodes, event data associated with a serviceassociated with the subscriber; reporting the event data to the mediatorunit; determining in the mediator unit a network-specific chargingalgorithm corresponding to the visiting network; and converting, in realtime, the event data in the mediator unit using the determinednetwork-specific charging algorithm to provide a charging data formatunderstandable to the billing unit, for updating of charging dataassociated with the subscriber between the mediator unit and the billingunit.
 2. The method of claim 1, wherein the network charging algorithmused in the mediator unit is subscriber-specific.
 3. The method of claim1, wherein a location of the mediator unit is associated with a charginggateway functionality, via which the event data is transferred to themediator unit.
 4. The method of claim 1, wherein the mediator unit isimplemented by using an intelligent network service control functionassociated with the telecommunications network nodes and the reportedevent data act as service triggers or the reported event data arereported in response to a request of the service control function. 5.The method of claim 1, wherein the billing unit is implemented using anintelligent network service control function and the mediator unittriggers the service.
 6. The method of claim 1, wherein the chargingdata is transferred from the mediator unit to the billing unit to updatethe charging data.
 7. The method of claim 6, wherein if the serviceassociated with the subscriber is a prepaid service and the billing unitincludes prepayment account data associated with the subscriber, a sumcorresponding to the charging data transferred to the billing unit issubtracted from the prepayment account at the billing unit and theservice associated with the subscriber is terminated when the prepaymentaccount balance is zero or negative.
 8. The method of claim 1, whereinif the service associated with the subscriber is a prepaid service andthe billing unit includes data indicating a prepayment accountassociated with the subscriber, a predetermined amount of the prepaymentaccount is transferred from the billing unit to the mediator unit, and,in the mediator unit, a sum corresponding to the charging data issubtracted from the transferred predetermined amount.
 9. The method ofclaim 8, wherein when the subscriber stops using the service, thetransferred predetermined amount remaining in the mediator unit istransferred back to the prepayment account at the billing unit.
 10. Themethod of claim 8, wherein when the transferred predetermined amountremaining in the mediator unit is exhausted, a new amount is transferredfrom the prepayment account at the billing unit to the mediator unit, orthe service associated with the subscriber is terminated if theprepayment account balance at the billing unit is zero or negative. 11.The method of claim 1, wherein the charging data format is expressed asan amount of money spent or as charging pulses.
 12. The method of claim1, wherein the billing unit comprising the subscriber's charging data islocated in the subscriber's home network.
 13. The method of claim 1,wherein the billing unit comprising the subscriber's charging data islocated in a subscriber identity module.
 14. The method of claim 1,wherein the billing unit comprising the subscriber's charging data islocated behind an open service architecture connected to the network.15. A billing system for charging a subscriber visiting in a visitedtelecommunications network other than a home network of the subscriber,the system comprising: a billing unit which comprises charging dataassociated with the subscriber and which is located outside the visitednetwork; a mediator unit; a telecommunications network comprising nodes,the nodes being configured to generate event data associated with aservice associated with the subscriber and to report the event data tothe mediator unit; and wherein the mediator unit is configured todetermine a network-specific charging algorithm corresponding to thevisited network and to convert, in real time, the generated event datausing the determined network-specific charging algorithm into a chargingdata format understandable to the billing unit for the updating of thecharging data associated with the subscriber between the mediator unitand the billing unit.
 16. The system of claim 15, wherein the networkcharging algorithm associated with the mediator unit issubscriber-specific.
 17. The system of claim 15, wherein the location ofthe mediator unit is associated with a charging gateway functionality,via which the event data is transferred to the mediator unit.
 18. Thesystem of claim 15, wherein the mediator unit is located in a CamelService Environment of a home network associated with the subscriber anda location of the billing unit is associated with an open servicearchitecture associated with the network.
 19. The system of claim 15,wherein the mediator unit is implemented using an intelligent networkservice control function associated with the telecommunications networknodes and the reported event data act as service triggers or thereported event data are reported at the request of the service controlfunction.
 20. The system of claim 19, wherein an IP protocol stack isassociated with an interface between the mediator unit and thetelecommunication network nodes.
 21. The system of claim 20, wherein theinterface between the mediator unit and the telecommunication networknodes is based on Common Object Request Broker Architecture.
 22. Thesystem of claim 15, wherein the billing unit is implemented using anintelligent network service control function, the mediator unittriggering the service.
 23. The system of claim 22, wherein a SignallingSystem Number 7 protocol stack is associated with an interface betweenthe mediator unit and the billing unit.
 24. The system of claim 15,wherein the mediator unit is configured to transfer the charging datacorresponding to a service associated with the subscriber to the billingunit for the updating of the charging data associated with thesubscriber.
 25. The system of claim 24, wherein if the serviceassociated with the subscriber is a prepaid service and the billing unitincludes data indicating a prepayment account associated with thesubscriber, and the system is configured to subtract from the prepaymentaccount a sum corresponding to the charging data transferred to thebilling unit and to terminate the service associated with the subscriberwhen the prepayment account balance is zero or negative.
 26. The systemof claim 15, wherein if a service associated with the subscriber is aprepaid service and the billing unit includes data indicating aprepayment account associated with the subscriber, and the system isconfigured to transfer a predetermined amount of the prepayment accountto the mediator unit and to subtract in the mediator unit a sumcorresponding to the charging data from the transferred predeterminedamount.
 27. The system of claim 26, wherein, when the subscriber stopsusing the service, the system is configured to transfer the remainingfrom the transferred predetermined amount in the mediator unit back tothe prepayment account at the billing unit.
 28. The system of claim 26,wherein, when the transferred predetermined amount remaining in themediator unit is exhausted, the system is configured to transfer a newamount from the prepayment account at the billing unit to the mediatorunit or to terminate the service associated with the subscriber if theprepayment account balance at the billing unit is zero or negative. 29.The method of claim 1, wherein the billing unit is located within a homenetwork associated with the subscriber, in a subscriber identity module,or behind an open service architecture connected to the network.
 30. Thesystem of claim 15, wherein the billing unit is located in a homenetwork associated with the subscriber or in a subscriber identitymodule.
 31. The system of claim 15, wherein the charging data format isexpressed as an amount of money spent or as charging pulses.
 32. Thebilling system of claim 15, wherein the billing unit comprising thesubscriber's charging data is located in the subscriber's home network.33. The billing system of claim 15, wherein the billing unit comprisingthe subscriber's charging data is located in a subscriber identitymodule.
 34. The billing system of claim 15, wherein the billing unitcomprising the subscriber's charging data is located behind an openservice architecture connected to the network.